A Land Manager's Guide to Improving Habitat for Forest Thrushes

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14 sites with Veeries were located in mixed forest, 44% in deciduous forest, and 1% in coniferous forest. The most common trees on sites occupied by Veeries were maples (73%), oaks (60%), pines (28%), American beech (21%), and hemlock (20%). Results from this study indicate that Veeries are most affected by the degree of fragmentation in the landscape and by the size of forest patches, especially the amount of “core forest” away from edges. The most suitable sites are also those with a denser deciduous shrub understory. Highest-suitability habitat only occurs in landscapes with at least 70% forest cover, and in these landscapes, patches larger than 1,000 acres (400 ha) are required (Table 1). Even in landscapes with 80% forest, patches of roughly 400 acres (165 ha) are required; minimum area is reduced to 127 acres (51 ha) if forest cover increases to 90%. Smaller forest patches in more fragmented landscapes do provide moderate habitat suitability, however, patches greater than 300 acres (120 ha) are still required in landscapes with 40% forest. Other studies suggest that Veeries use a variety of habitats in different parts of their range. In New York State, Veeries select early successional forest for breeding (Kendeigh 1945, 1946). In highland areas of North Carolina, it’s a bird of mature oak forest (Odum 1950) and on Apostle Island in Wisconsin, it’s found primarily in aspen and red oak forests where the understory is most dense (Beals 1960). In New Jersey, Veeries prefer moist forests that are 40–60 years old with a dense understory (Suthers 1987–1988). Unlike the other forest thrushes, Veeries show a strong tolerance for disturbed forest with a well-developed understory (Dilger 1956). Noon et al. (1976) found that Veeries bred in 77% of available disturbed and successional forests, but only 18% of mature Table 1. Minimum area required to provide high, moderate, or low habitat suitability for Veery based on analysis of 685 study sites in the East/ Midwest region (see page 11 for definitions of habitat suitability). Percentage of forest in 2,500-acre block Minimum area (acres) required for High Moderate Low 90 127 3 Any size 80 396 10 Any size 70 1004 26 Any size 60 NA a 61 1 50 NA 136 2 40 NA 305 4 30 NA 708 9 20 NA NA 24 10 NA NA 74 a Not Available—acreage values exceed the amount of forest in the 2,500-acre block. undisturbed habitat. Bertin (1977) suggested that in mature woodlands, moisture regime was the primary factor driving habitat selection, with the dampest areas occupied first and pointed to available shrub cover as the most critical habitat component. Veeries may benefit from selective harvesting that opens up the canopy and allows the understory to develop (Webb et al. 1977, Thompson and Capen 1988). Derleth et al. (1989) found that Veeries tolerated small clearcuts (2– 20 acres or 1–8 ha), but Morgan and Freedman (1986) noted that Veeries were absent from large clearcuts for six years following the harvest. Habitat selection may vary when other thrushes are present. In many portions of their range, Veery breed primarily in deciduous forest, even when coniferous forest is available. In a study conducted in Tennessee, in areas where their breeding range overlapped with Swainson’s Thrush, the Veery used deciduous, coniferous, and mixed forests (Noon 1977). Although it was once absent from higher elevation spruce forests in the Appalachian Mountains, Veerys have expanded into the southern Appalachian spruce forests when congeners are not present (Noon 1981). Hermit Thrush In the East/Midwest Forest Region, Hermit Thrushes are restricted largely to the northernmost portions and also to higher elevations through the Appalachians where coniferous forests are dominant. Small populations occur in other coniferous habitats at lower elevations, including cedar swamps, hemlock ravines, conifer plantations, and pine barrens. Although this thrush is common and apparently increasing, it is nonetheless shown to be highly area sensitive and intolerant of forest fragmentation within its range. In the Birds in Forested Landscapes study, Hermit Table 2. Minimum area required to provide high, moderate, or low habitat suitability for Hermit Thrush based on analysis of 347 study sites in the East/Midwest region (see page 11 for definitions of habitat suitability). Percentage of forest in 2,500-acre block Minimum area (acres) required for High Moderate Low 90 32 5 Any size 80 56 9 1 70 88 14 1 60 132 22 2 50 196 32 3 40 289 47 4 30 435 71 6 20 NA a 111 10 10 NA 193 18 a Not Available—acreage values exceed the amount of forest in the 2,500-acre block.
Thrushes were detected at 142 (26%) of 553 sites surveyed in the East/Midwest region. Seventy-seven percent of sites with Hermit Thrushes were located in mixed forest, 20% in deciduous forest, and 2% in coniferous forest. The most common trees present at sites occupied by Hermit Thrush were maples (75%), oaks (53%), pines (41%), hemlock (32%), and beech (27%). Results from this study indicate that Hermit Thrushes are most attracted to forests with a high coniferous component, and they avoid sites with a largely deciduous shrub understory. They are also area sensitive, although less so than the Veery or Wood Thrush. In highly fragmented landscapes, single large forest patches may still offer highly suitable habitat for Hermit Thrush (Table 2), and even in more intact (50% forest) landscapes, patches roughly 200 acres (80 ha) in size are required. Smaller forest patches do offer moderately suitable habitat, especially if they contain the conifers. In New York, Hermit Thrushes selected sites in dry coniferous, mixed, or deciduous forests and were sometimes associated with internal forest edges (Andrle and Carroll 1988, Dilger 1956). In forest communities in northwestern Wisconsin the abundance of Hermit Thrushes was related to the amount of edge and variables relating to patch shape (Hawrot and Niemi 1996). Researchers compared two harvest techniques in riparian areas of northern Wisconsin (full tree harvest and cut-to-length (CTL)). Bird surveys one year prior to harvest and three years after harvest showed that bird communities were affected by both harvest types. Hermit Thrush, along with Ovenbird and Black-throated Green Warbler showed significant declines. Within three years of harvest no individuals of these species were observed (Hanowski et al. 2003). Management Summary for the East/Midwest Forest Region Landscape Level In this region, the primary consideration for all thrush species is the maintenance of large contiguous forest patches that promote reproductive rates that compensate for adult and nestling mortality. Thrushes in this region will tolerate and may even benefit from patch-level disturbances such as light selective harvesting that does not contribute to forest fragmentation. The Veery and Wood Thrush are the most area sensitive of the three species in this region and thus set the bar for minimum forest size. The required forest patch size needed for consistent successful reproduction is highly related to surrounding land use (see Tables 1 and 2); in general however, forest patches of 150 acres (62 ha) or larger will be adequate to provide moderate levels of habitat suitability, except in landscapes with little forest. In landscapes with greater than 50% forest, smaller woodlots can provide suitable habitat. In highly fragmented forests or landscapes with very little forest cover, minimizing edge and increasing connectivity among forest patches may increase habitat quality in small patches. For Veeries, maximize core forest by reducing the amount of edge habitat associated with forest fragments. This can be done by managing patch shape, creating transitional, as opposed to abrupt edges, and reforesting areas between disconnected patches. In lowlands, especially in damp sites, management should focus on Wood Thrush; at higher elevations and in moist, mixed forests management should focus on both Veeries and Wood Thrushes; and in mostly coniferous forests and on drier sites, management should focus on Hermit Thrushes. Site Level For Wood Thrush and Veery, create and maintain forest habitat with a dense understory of deciduous saplings and shrubs. Because of its area sensitivity, focus site-level management for Wood Thrushes on patches greater than 200 acres (80 ha). This can be accomplished by planting appropriate native trees and shrubs, creating gaps in the canopy that permit sunlight to reach the forest floor, and controlling browsing by white-tailed deer and livestock. Moderate selective harvesting of timber is often tolerated by thrushes, and serves to increase the shrub layer. Clear cutting and heavy selective cutting are not recommended for thrush management. Hermit Thrush prefer a strong coniferous component and may benefit from conifer plantings or silvicultural practices that favor existing conifers, especially pines and eastern hemlock. Protecting stands of hemlock and cedar swamps within hardwood forests, as well as protecting large areas of pine-barrens habitat will also benefit Hermit Thrushes. 15
Page 1 and 2: A Land Manager's Guide to Improving
Page 3 and 4: A Land Manager’s Guide to Improvi
Page 5 and 6: Figure 1. Vast coniferous forests o
Page 7 and 8: Managing the Contemporary Forest Th
Page 9 and 10: General Guidelines: Key Forest Char
Page 11 and 12: Landscape Context Effects The amoun
Page 13 and 14: Regional Management Guidelines for
Page 15: niferous forest. The most common tr
Page 19 and 20: are most abundant in northern hardw
Page 21 and 22: Western Forest Region Description W
Page 23 and 24: and abundance in uncut forests, for
Page 25 and 26: Swainson’s Thrush (Catharus ustul
Page 27 and 28: Wood Thrush (Hylocichla mustelina)
Page 29 and 30: Literature Cited Andrle, R.F. and J
Page 31 and 32: communities. Pp. 33-48 in Proceedin

A Land Manager's Guide to Improving Habitat for Forest Thrushes

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